Metyrosine, which has the structure of Formula:
is useful in reducing elevated levels of catecholamines associated with pheochromocytoma, and preventing hypertension. Metyrosine, as shown, is a chiral compound. The synthesis of metyrosine in pure or substantially pure enantiomeric form requires a process that involves using substantially diastereomerically and/or enantiomerically pure intermediates. The Applicant has discovered, surprisingly, certain compounds that are substantially diastereomerically or enantiomerically pure and processes to prepare them, and which compounds may be converted to metyrosine.